Backhoe swings right, but not left

[rScotty]

I really don't know what happened, but I am guessing a cup seal caught the flow and thereby got reinforced.

But I really don't even know if it has cup seals in the cylinders. I don't know how it is piped. I don't know if it is in parallel (one piston side in parallel with the rod of the other cylinder, etc.) I used to tell folks that telling me what they don't know is not helping...so I will heed my own advice and stop right there.

I was wondering if I was talking out of my hat with my analysis, but I have found a hydraulic diagram that supports my theory buy searching "backhoe hydraulic diagram" on Google.

HYDRAULIC SYSTEM DIAGRAM (SERIAL NUMBERS 319995 THRU 342573 ONLY)

Compare that diagram to my comments earlier, and do tell us if it matches yours (vis a vis the swing cylinders only), if you don't mind.

Hey, Thanks for that hydraulic system diagram. What is that one for?
As for the series versus parallel swing cylinders. The M59 is similar to what you referenced. Near as I can tell, the M59 works the same way in that the piston side and rod sides of opposite cylinders are pressurized at the same time. Doing it that way doubles the force, moderates the flow, and probably makes it smoother....but does make it difficult to visualize how the swing could only be powered in only one direction no matter what happens with the cylinders.

I'm not that familiar with fancy construction equipment hydraulic systems, just with the older open circuit tractor type. In comparison with the basic one in that diagram you referenced, the M59 is much more complex. It is more sophisticated than anything hydraulic I've ever dealt with.

The backhoe controls alone have 8 or 10 hi-tech dual stage adjustable & expensive relief valves (all identical) which I've ever seen on a backhoe control. One for each motion. Plus several load checks for things like the stabilizer legs.
Instead of using a single big hydraulic pump with flow proportioning circuits, the M59 has completely separate additional hydraulic pumps for different hydraulic circuits - looks like three in all. Not counting the HST tranny. The swing system has its own separate hydraulic pump. All this complexity and mine doesn't even have the accessory rear hydraulic outlets. I'm glad for that! Just has the optional bucket thumb - which of course has its own control and associated relief valves.
They sure didn't spare themselves any complexity on the backhoe operation. In their defense, I'll say that the controls do have a very good "touch".
Thanks for all the help, rScotty

 

[oldnslo]

rscotty.
is there any way you can post a copy of the schematic for this BH. If this uses pressure compensated controls or load sense control one of the sense lines could have stuck open and then by the repeated use flushed itself out. If the load sense line does not connect or send a signal to the pump you will not build any pressure above standby. Not sure how much pressure it takes to move the swing on a back hoe.

Roy

 

[EE_Bota]

Hey, Thanks for that hydraulic system diagram. What is that one for?
As for the series versus parallel swing cylinders. The M59 is similar to what you referenced. Near as I can tell, the M59 works the same way in that the piston side and rod sides of opposite cylinders are pressurized at the same time. Doing it that way doubles the force, moderates the flow, and probably makes it smoother....but does make it difficult to visualize how the swing could only be powered in only one direction no matter what happens with the cylinders.

I'm not that familiar with fancy construction equipment hydraulic systems, just with the older open circuit tractor type. In comparison with the basic one in that diagram you referenced, the M59 is much more complex. It is more sophisticated than anything hydraulic I've ever dealt with.

The backhoe controls alone have 8 or 10 hi-tech dual stage adjustable & expensive relief valves (all identical) which I've ever seen on a backhoe control. One for each motion. Plus several load checks for things like the stabilizer legs.
Instead of using a single big hydraulic pump with flow proportioning circuits, the M59 has completely separate additional hydraulic pumps for different hydraulic circuits - looks like three in all. Not counting the HST tranny. The swing system has its own separate hydraulic pump. All this complexity and mine doesn't even have the accessory rear hydraulic outlets. I'm glad for that! Just has the optional bucket thumb - which of course has its own control and associated relief valves.
They sure didn't spare themselves any complexity on the backhoe operation. In their defense, I'll say that the controls do have a very good "touch".
Thanks for all the help, rScotty

Wow it DOES sound complicated. I am not sure what that diagram I posted was for, I only meant it to be for talking purposes as an example of the swing circuit I was imagining...just wanted some proof to myself that such a circuit even existed.

But for talking purposes...imagine that when one direction is powered, due to the parallel path, only one cup on one side of one cylinder needs to leak badly, and all the flow will go there, and the thing may not move. But in the other direction, the other cup side is used for each cylinder, and it moves just fine.

I'm not saying that is what was wrong...it works now...but we WERE looking for ideas about what could be wrong, and how to know which cylinder it is, etc. If you look at the diagram again, a man could simply switch the hoses at the valve, and if the thing then swings the OTHER direction but not the previous (that used to work fine) then it is not the cylinders, but in the valving.

All I am doing is trying to help sort testing methods to diagnose the problem should it recur.

Your valving does sound complicated, but I wonder if it is not pretty conventional, but maybe with some flow control adjustments added, etc.

Did you misspeak when you said it has a separate pump for the swing...did you mean a separate pump for the entire backhoe, or did you truly mean a separate pump for swinging the boom?

 

[boggen]

Kubota Tractor Corporation - Parts List
typed in "M59" clicked search
list came up, and only showed "BT1200 / BT1200V" as optional backhoe for M59, clicked that new window opened up.

it is showing both swing cylinders running in parallel. diagram showing a Tee adapter on both cylinders for how hoses run.

looking at diagrams a little more. would the "nut" on end of the rod. that goes into the cylinder tube, possibly come loose enough to let the seals, leak oil around them? more of a load on swing cylinders more of a leak and possibly causing seals to bunch up letting leak happen non stop? perhaps working the backhoe left and right to swing it. was enough to re-seat the seals.

and then come next time when a bigger load is placed on the cylinder and it happens again...?

================
looking a bit more at diagrams, more so at the valve / spool that controls the swing of the backhoe. is it possible, for one of the 0-rings on the rod that moves up and down through spool/valve to roll off some how, and is now re-seated? perhaps the 2 bolts that hold the main rod in the valve. came a little loose allowing some additional play within the valve/spool. letting hyd oil to by pass. vs letting oil goto correct path to swing the backhoe?

 

[TBarD]

The M59 does have a separate swing pump. The main hydraulic pump powers the boom/dipper/bucket (and loader etc.). The main hydraulic pump has a separate section for the power steering, hence the tractor essentially has three hydraulic pumps.

It could be that there was foreign matter in the valve, preventing it from fully opening in one direction. Moving the lever and swinging the boom back and forth may have eventually cleared it out, allowing normal flow.

 

[rScotty]

Wow it DOES sound complicated.

But for talking purposes...imagine that when one direction is powered, due to the parallel path, only one cup on one side of one cylinder needs to leak badly, and all the flow will go there, and the thing may not move. But in the other direction, the other cup side is used for each cylinder, and it moves just fine.

I thought about that, but came to the conclusion that it was unlikely for any leak to be able to pass fluid faster than the pump could supply it at full rev.....so my "rule to thumb" for leaking problems is no movement at low rpm, but that at high enough rpm there will be some movement. What do you think?

IF you look at the diagram again, a man could simply switch the hoses at the valve, and if the thing then swings the OTHER direction but not the previous (that used to work fine) then it is not the cylinders, but in the valving.

Ahhh!!..That's a very good idea. I've done the swapping things across before, but missed that it would work on this system. It is a good way to diagnose.

Your valving does sound complicated, but I wonder if it is not pretty conventional, but maybe with some flow control adjustments added, etc.

Yes, and what I was trying to say is that the complexity seems to be more in the application than in the design. Hydraulically, it is a typical constant displacement open-circuit design. Complexity is usually reserved for closed circuit designs with their pressure accumulators and variable flow rate pumps. But the individual parts in the M59 system show a lot of care. Even things like the relief valves are quite complicated. My old American-made hydraulic control valves all had a relief valve that was basically a shimmed spring which pushed a steel ball bearing against a hole. This Kubota relief valve is a giant step more sophisticated..

Did you misspeak when you said it has a separate pump for the swing...did you mean a separate pump for the entire backhoe, or did you truly mean a separate pump for swinging the boom?

Yes, the swing has it's own completely separate pump from the boom and bucket functions. There's the that complexity again. You can P1 and P2 in some of the picture below from the shop manual.

I uploaded some nice pictures that Oldnslo asked about. This is an interesting hydraulics discussion. Take a look at the modern M59 workshop manual versus some of the old hand-drawn workshop drawings (Yanmar)!!
rScotty

 

[EE_Bota]

Yes, the swing has it's own completely separate pump from the boom and bucket functions. There's the that complexity again. You can P1 and P2 in some of the picture below from the shop manual.

I uploaded some nice pictures that Oldnslo asked about. This is an interesting hydraulics discussion. Take a look at the modern M59 workshop manual versus some of the old hand-drawn workshop drawings (Yanmar)!!
rScotty

I will look at it more tonight, but so far, it is interesting that both pumps contribute to most functions(wrong), but only the one pump does the boom swing(right). Whether a piston leak could consume all flow depends on the actual flow of that pump...but I would not be surprised either way since booms need to swing fairly slowly, else a person could extend a full scoop way out and really make a heck of a crowbar out of a full extended hoe arm...a man might be able to twist off a stabilizer or do all sorts of crazy stuff if that boom start whipping side to side (edit: and the reliefs would protect the system, but not stop the momentum.)

Some of the additional complexity is a relief valve for each circuit. The reliefs could participate in a problem, and could participate in the problem you were having. Switching the lines can still be diagnostic, but I will have to consider it a bit further...since there are free flow back checks associated with the reliefs, and I haven't figured out what they enable. I have seen them before, but I always have to apply their appearance to the actual function of the apparatus to see what they help. They could allow free wheeling, etc.

It is complicated, but I bet that thing is pretty sweet too.

Later tonight, I may have to print those drawings out and mark on them to begin to understand all of the possibilities, but folks good at hydraulics are probably snickering at me. I hope so...a good chuckle is always a good thing.

Edit..nope, I'm wrong...the swing doesn't contribute to anything else, that is a tank line. I don't know what to make of the check, since it free flows from tank to the cylinders, but blocks the ports otherwise..allowing only the relief to function. It could be a start up thing or a means to be sure that if the boom is pushed sideways so hard that that it cracks the relief, the other side can have makeup oil from tank to avoid sucking in air at the seal, or water or cause cavitation. I think we can ignore those checks completely unless faulty. Switching the hoses is valid, and will not harm anything, but the diagnosis is blurred...since it need not be a cylinder, but could be the relief too or the check stuck open due to debris. If I figure something else out I will post, but looking at it more tonight may not reveal new info since I think I now have it mostly figured.

 

[oldnslo]

rscotty,
Thanks for posting the schematics. Would suspect one of the reliefs got stuck open. These relief valves are there to protect from shock or surges caused by the sudden stopping of a swing function. The inertia of the boom and bucket can cause intense pressure spikes. The check valves in the RV's are to allow the cylinders to draw in oil (prevent cavitation) while moving under vacuum in the above scenario.

The reason for a separate pump for swing is for consistent motion regardless of the other functions on BH. This is a safety concern when operating around people or buildings.

Roy

 

[EE_Bota]

rscotty,
Thanks for posting the schematics.

Roy

Agreed..thanks...I liked looking at what the cool hydraulics setups look like. I know why mine is so jerky, and now I know how they make them less jerky.

oldnslo...thanks for the info about the separate pump being about safety due to consistent movement of the swing. I had not thought of that, and it is good to know.

 

[MarkV]

Just to cover all bases...are the hydraulic fluids full...is it due for a filter change...did you recently replace anything that could have allowed air into the system?

MarkV